1. Field of the Invention
The present invention relates to a light-emission controlling apparatus disposed in an automobile or the like, for changing a light-emission mode of a light-emitting device such as an electric discharge lamp such as a high-voltage sodium lamp, or a metal halide lamp, or an incandescent lamp so that the light-emitting device switches between different light-emission modes.
2. Description of the Prior Art
Referring now to FIG. 10, there is illustrated a schematic diagram showing the structure of a prior art light-emission controlling apparatus disclosed in Japanese Patent Application Laying Open (KOKAI) No. 6-243979. In the figure, reference numeral 5 denotes an electric discharge lamp, 8 denotes a switch, 9 denotes a voltage detecting circuit having a terminal connected to a point of connection between capacitors 4b and 4c via the switch 8, for detecting a voltage across the electric discharge lamp 5 after an electric breakdown is produced in the electric discharge lamp 5, 11 denotes a current detecting circuit for detecting a current flowing through the electric discharge lamp 5, and 12 denotes an electric-breakdown detecting circuit for detecting a current which can rush into the electric discharge lamp 5 when an electric breakdown is produced in the electric discharge lamp 5 so as to generate a signal indicating whether or not an electric breakdown is produced.
Furthermore, reference numeral 13 denotes a control unit implemented via a microcomputer or the like, for switching on or off the switch 8 and for controlling the frequency of a signal delivered to an inverter circuit 2 according to signals from the voltage detecting circuit 9, the current detecting circuit 11, and the electric-breakdown detecting circuit 12, and 15 denotes an alarm lamp through which the control unit 13 can warn a user when it determines that the value of the lighting voltage across the electric discharge lamp 5, which is informed by the voltage detecting circuit 9, is not within the range of lighting voltage ratings.
In operation, when the light switch is turned on and an electric breakdown is produced in the electric discharge lamp 5, a current rushes into the electric discharge lamp 5. Then the electric-breakdown detecting circuit 12 detects the current rushing into the electric discharge lamp 5 and then furnishes a pulse indicating that an electric breakdown is produced to the control unit 13.
In response to the pulse from the electric-breakdown detecting circuit 12, the control unit 13 reads the value of the voltage across the electric discharge lamp 5 which is converted by the voltage detecting circuit 9 and compares the current value of the voltage across the electric discharge lamp with the minimum value of the lighting voltage ratings of the electric discharge lamp 5 which was preset to the control unit 13. If the control unit 13 determines that the current value of the voltage across the electric discharge lamp 5 is lower than the minimum value, it causes the alarm lamp 15 to light up.
By way of contrast, if the control unit 13 determines that the current value of the voltage across the electric discharge lamp 5 is greater than or equal to the minimum value of the lighting voltage ratings of the electric discharge lamp 5, it further compares the current value of the voltage across the electric discharge lamp to the maximum value of the lighting voltage ratings of the electric discharge lamp 5 which was preset to the control unit 13. If the control unit 13 determines that the current value of the voltage across the electric discharge lamp is greater that the maximum value, it causes the alarm lamp 15 to flash on and off.
Since the prior art light-emission controlling apparatus is constructed as mentioned above, there is a problem in that if an error arises in the detected value of the voltage across the electric discharge lamp, which shows the light-emission state of the electric discharge lamp, the light-emission controlling apparatus can immediately warn the user that the value of the voltage across the electric discharge lamp is not within the range of lighting voltage ratings.
Another problem with the prior art light-emission controlling apparatus is that since the user must consciously watch the alarm lamp disposed in addition to the electric discharge lamp, there is a possibility that the user fails to notice the warning.